DESCRIPTION: The partitioning of target molecules between uniform liquids and two-dimensional organic monolayer and bilayer systems forms the basis for a wide diversity of processes that are central to biological function. Such selective sorption behavior is also the basis for many high-efficiency separation techniques and sensor designs of key interest in the analysis of complex mixtures of biochemical import. In the proposed study, we will design and fabricate well-controlled monolayer arrays to systematically determine the effects of interfacial structure on solute partitioning processes. These alkyl arrays will allow control of chain density in both the lateral and radial domains, creating the well-defined interface necessary for the fundamental studies of liquid-interphase partitioning. Such fundamental partitioning studies have significant implications for processes as diverse as anesthetic action and protein folding. Moreover, these molecular arrays contain a delocalized polymer backbone capable of acting as an interaction transducer in the design of sensor systems. The proposed studies interleave these functionalities, creating unique molecular interfaces that allow the simultaneous measurement of fundamental interfacial partitioning and act as interaction transducers. The polydiacetylene (PDA) family of molecules will be utilized in the fabrication of these molecular assemblies. Using self-assembly techniques, diacetylene disulfide molecules form well-defined arrays on gold surfaces and may be subsequently photopolymerized to fabricate robust monolayer structures. Chain density in the lateral and radial domains is accomplished by coadsorption of varying chain length diacetylenes. The role of defect sites in the partitioning processes will be assessed using reductive desorption processes to form defect sites of varying size and number density. In all cases, a multi-faceted approach to structural characterization will be undertaken simultaneously with partitioning measurements. Concurrent with partitioning studies, the transducer properties of these monolayer polymers will be investigated. A delocalized electronic backbone resides within these interfacial structures. adding structural robustness as well as the potential for signal response from interfacial interactions. Although the exact nature of the color change in PDA systems is not yet fully understood, perturbation of the extent of delocalization within the electronic structure of the polymer backbone gives rise to significant alterations in the frequency of the _A_* transition. We propose to exploit this perturbational color change in the design of a family of interaction based sensors. We believe that this interwoven approach to fundamental studies of partitioning and sensor design will have significant implications for separation processes as they occur in nature and as they are designed by human beings.